Information About the Path Selection Metric for MPLS TE Tunnels

Certain tunnels carry voice traffic, which requires low delay, and other tunnels carry data.You can configure the path selection metric for TE tunnels on a global or per-tunnel basis. You can specify the TE link metric on an interface, or let it default to the IGP link metric. You can also specify the link metric for path selection for these low-delay traffic tunnels and let the other tunnels use the Interior Gateway Protocol (IGP) metric for path selection. MPLS TE supports Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) as the IGP.

IGP floods two metrics for every MPLS TE link as follows:

IGP link metric, which is the IGP determined metric for the link.

Path selection metric, which is the TE link metric for the link. This metric defaults to the IGP link metric, but you can specify the TE link metric by using the mpls traffic-eng administrative-weight command on the interface.

Configurable path selection metric for tunnels requires an MPLS license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the
Cisco NX-OS Licensing Guide.

Prerequisites for the Path Selection Metric for MPLS TE Tunnels

The path selection metric for MPLS TE tunnels has the following prerequisites:

Guidelines and Limitations for the Path Selection Metric for MPLS TE Tunnels

The path selection metric has the following configuration guidelines and limitations:

Unless explicitly configured, the TE link metric (administrative-weight) for a given link is the IGP link metric. When the TE link metric is used to represent a link property that is different from the cost/distance, you must configure every network link that can be used for TE tunnels with a TE link metric that represents that property. Failure to do so might cause tunnels to use unexpected paths.

MPLS TE supports only a single IGP process or instance. Multiple IGP processes or instances are not supported and you should not configure MPLS TE in more than one IGP process or instance. You might configure MPLS TE in multiple OSPF areas or both IS-IS levels.

Prerequisites

Ensure that you are in the correct VDC (or use the
switchto vdc
command).

SUMMARY STEPS

1.
configure
terminal

2.
mpls traffic-eng configuration

3.
path-selection metric
{
igp
|
te
}

4. (Optional)
show mpls traffic-eng tunnels
tunnel-te
number

5. (Optional)
copy running-config startup-config

DETAILED STEPS

Command

Purpose

Step 1

configure
terminal

Example:

switch# configure terminal

switch(config)#

Enters global configuration mode.

Step 2

mpls traffic-eng configuration

Example:

switch(config)# mpls traffic–eng configuration

switch(config-te)#

Enters MPLS TE configuration mode.

Step 3

path-selection metric
{
igp
|
te
}

Example:

switch(config-te)# path-selection metric te

Specifies the metric type to use if a metric type is not explicitly configured for an MPLS TE tunnel. If you configure the TE path selection metric type, you can also configure the MPLS TE administrative weight on each TE tunnel. The default is IGP.

(Optional) Copies the running configuration to the startup configuration.

Configuring the Path Selection Metric Type for a TE Tunnel

You can override the global tunnel path selection metric on a per-TE tunnel interface, and you can also override the IGP link metric on any link by configuring the TE administrative weight on that link.

SUMMARY STEPS

1.
configure
terminal

2.
interface
tunnel-te
number

3.
path-selection metric
{
igp
|
te
}

4. (Optional)
interface
type/
number

5. (Optional)
mpls traffic-eng administrative-weight
weight

6. (Optional)
show mpls traffic-eng tunnels
tunnel-te
number

7. (Optional)
copy running-config startup-config

DETAILED STEPS

Command

Purpose

Step 1

configure
terminal

Example:

switch# configure terminal

switch(config)#

Enters global configuration mode.

Step 2

interface tunnel-te
number

Example:

switch(config)# interface tunnel-te 1

switch(config-if-te)#

Enters TE interface configuration mode. The
number
range is from 0 to 65503.

Step 3

path-selection metric
{
igp
|
te
}

Example:

switch(config-if-te)# path-selection metric te

Specifies the metric type to use for the MPLS TE tunnel path selection. The default is TE.

Step 4

interface
type/nu
mber

Example:

switch(config-if-te)# interface ethernet 2/1

switch(config-if)#

(Optional) Enters interface configuration mode. Use
?
to see a list of supported interfaces.

Step 5

mpls traffic-eng
administrative-weight
weight

Example:

switch(config-if)# mpls traffic-eng administrative weight 20

(Optional) Overrides the IGP administrative weight (cost) of the link. Configure this parameter if you configured the path selection metric type as TE and you want to specify the TE link cost/administrative-weight rather than defaulting to the IGP cost.

The section shows how to configure the link metric type that you can use for the tunnel path selection and how to configure the link metrics. The configuration commands included in this section allow you to specify the metric type for path selection and assign metrics to links. Additional commands are required to fully configure the example scenario. For example, you need the IGP commands to continue TE and the link interface commands to enable TE and specify the available bandwidth.

The example in this section supports the simple network technology shown in Figure 14-1.

Note This example applies only to dynamic tunnels, not to ones with an explicit path.

The path selection for Tunnel1 and Tunnel3 should use a metric that represents a link delay because these tunnels carry voice traffic.

The path selection for Tunnel2 should use IGP metrics because MPLS TE carries data traffic with no delay requirement.

The following configuration fragments for each of the routers show the configuration that relates to link metrics and their use in the tunnel path selection. TE metrics that represent a link delay must be configured for the network links on each of the routers, and the three tunnels must be configured on R1.

These configuration fragments force Tunnel1 to take path R1-R3-R4, Tunnel2 to take path R1-R2-R4, and Tunnel3 to take path R1-R3-R4-R5 (if the links have sufficient bandwidth to accommodate the tunnels).